Glaucoma is a family of diseases of the eye which is characterized by increased intraocular pressure. If left untreated, over time glaucoma causes progressive and irreversible damage to the optic nerve, with associated loss of the midperipheral vision which then subsequently spreads into the far peripheral vision as well as the central vision. Severe cases of this disease usually result in blindness if adequate control of intraocular pressure is not achieved.
Historically, a variety of approaches have been used to treat glaucoma, namely topical medications, oral medications, lasers and surgical procedures designed to create a fistula for the aqueous humor in the eye to the external surface of the eye. The common goal of all of these modalities is to reduce intraocular pressure and thereby prevent progressive damage. Surgical treatment of glaucoma has a long history pre-dating the twentieth century. The means of surgical treatment have been varied and numerous, although none have succeeded entirely satisfactorily in lowering intraocular pressure, and in minimizing the risks of complications associated with these various procedures which in and of themselves may be vision threatening.
In general, glaucoma is treated surgically only when other treatment measures have failed. Usually surgical treatment involves the creation of a simple fistula by incising an opening in the anterior chamber angle to allow the free flow of aqueous into the subconjunctival space. The procedure is reasonably successful with approximately seventy-five percent of the patients having adequate pressure control for five years. The most frequent cause of failure is external scarring of the opening which occludes the flow of fluid out of the eye and results in a return to a state of increased intraocular pressure.
A second attempt at fistulization may be performed with or without the use of chemical agents which retard external scarring. The chemical inhibitors of scar tissue are usually not used on initial procedures because of an associated risk of increased postoperative complications. The success rate of such second attempts is approximately sixty percent.
Many patients unfortunately still fail multiple standard filtering operations. Intermittently over the last fifty years, the use of a tube or shunting device to transport aqueous farther posteriorly where scarring would be less likely to occur has been attempted in an effort to offer treatment to those who in the past frequently only went blind because of the scarring of the openings made by the standard surgical treatment(s). This class of devices is known as setons.
Setons have been made available in numerous sizes, shapes and configurations. Prior to the advent of microsurgery, these devices often were made of a myriad of materials including metallic substances which frequently eroded into the eye or extruded from the eye and therefore many of these attempts, especially those of the 1950s and 1960s, were abandoned because of unacceptable complications associated with the procedure. Newer glaucoma seton devices have gained in popularity given the markedly improved results they achieve, however, these newer devices still present numerous problems.
Regarding the newer seton devices commercially available, significant complications of surgery which require second operations occur in approximately thirty to thirty-five percent of cases in the immediate peri-operative period. Many of these devices are cumbersome, difficult to implant, require multiple procedures as part of the general strategum for implantation or are not premanufactured and require manufacture by the surgeon prior to implantation.
For example, one such newer implant device for the drainage of aqueous humor in the treatment of glaucoma was disclosed by Molteno in U.S. Pat. Nos. 4,750,901 and 4,457,757. According to Molteno, an implant comprised of a rigid circular plate having an upper ridge and a subsidiary ridge is sutured to the sclera of an eye. A tube connected to the implant is passed through the sclera to the anterior chamber of the eye to drain aqueous humor from the anterior chamber into the circular space formed by the plate and, from there, into the subconjunctival space. Molteno also discloses in U.S. Pat. No. 4,457,757 a pair of plates to increase the surface area required for proper drainage of aqueous humor.
The Molteno implant presents a number of problems. This implant is comprised of a large, rigid, flat plate which is not designed to fit on the globe of the eye given that the globe is spherical and the implant is flat. The Molteno implant has a tendency to stretch and tear fragile conjunctival mucous membranes because of its rigidity and lack of contoured shape. Also, the Molteno device requires a minimum of two sutures anteriorly at positions designated 10 and 20 of the Molteno patents and, therefore, the posterior aspect of the plate has a tendency to be excessively mobile after implantation.
Additionally, the Molteno device comes in single and double plate variations. The single plate device seems to work reasonably well early, but fails late in a high percentage, approximately fifty percent, of patients. The second generation double plate device avails a larger surface area for drainage. Unfortunately, it is much more difficult to install surgically than the single plate, requiring multiple (at least four) sutures to implant, thereby complicating the surgery given that each suture pass potentially dangerous. Furthermore, the surgeon installing the double plate is required to open up the entire superior 200 degrees of the eye in order to install it properly. Also, the tube which connects the two plates was intended initially to pass underneath the superior rectus muscle, but this is technically impossible in most cases and therefore a plastic tube is allowed to rest exterior to the superior rectus muscle and is at risk for extrusion.
Compared to the single plate, the double plate Molteno implant has a lower rate of late failure, approximately twenty-five percent. However, recent literature shows that both Molteno devices restrict ocular movement and cause double vision in patients because of their rigidity and size. The implant essentially traps the extraocular muscles which move the eye and creates blocks to the smooth excursion of the globe, thereby causing misalignment of the eyes and double vision.
Although the Molteno implants have been one of the most commercially successful of all glaucoma drainage devices, the problems with the Molteno implants are significant. The Molteno implant utilizes an implant design which essentially is not biocompatible with its implant environment and which tends to result in multiple complications associated with its implantation. This requires multiple modifications by the surgeon in implantation, thus making it difficult to employ. It requires the most highly skilled ophthalmic surgeons to utilize it effectively, and even then presents significant problems. Finally, the tube of this device, and all others which do not restrict access of flow of fluid early in the postoperative period, results frequently in early hypotony or exceedingly low intraocular pressures which induces significant early postoperative complications. Surgeons have modified the device by ligating the silastic tubing which connects the anterior chamber to the plate with a rapidly dissolving suture material to try to blunt this adverse effect. The amount of pressure required for the ligature is thereby left to the technical skills of each individual surgeon and therefore produces erratic results with regard to early pressure reduction in patients implanted with this device.
Other glaucoma implant devices have been utilized to drain aqueous humor from the anterior chamber of the eye to reduce intraocular pressure. For example, Shocket discloses in U.S. Pat. Nos. 4,826,478 and 4,722,724 an implant device and surgical technique for treating neovascular glaucoma using an anterior chamber tube shunt and a silicone band which is positioned to encircle the globe of the eye. According to Shocket, the silastic tube is cradled on the silicone band, with one end of the tube positioned into the anterior chamber.
The Shocket device and procedure present a number of problems. First, the device must be assembled by the surgeon prior to the procedure, which process is extremely labor-intensive. The device is not manufactured in its appropriate configuration and this leads to considerable inherent variations in the device as implanted. Second, the implantation of the device requires dissection of the entire circumference of the globe and disruption of structures which ultimately need not be manipulated in order to implant a device which would create a posterior reservoir for the drainage of aqueous humor. Third, the Shocket procedure requires multiple sutures in all quadrants of the globe in order to firmly attach the silicone band to the sclera. Fourth, the device requires ligation of the silastic band to prevent early post-operative hypotony by the surgeon at the time of the procedure. Fifth, the Schocket procedure is designated a multiple piece device which in recent studies have been found to be less successful in the management of intractable glaucoma than single piece devices such as the present invention. See Lavin, Franks, Wormlawd and Hitchings, Archives of Opthalmoloqy, Volume 110, April 1992, pages 480-485.
Others have disclosed various devices and procedures for treating glaucoma through implants that drain aqueous humor. Many of these efforts have been attempted to address the problems of hypotony, fibrosis and other complications caused by implanting glaucoma drainage devices. These include Krupin on valve implants and filtering surgery, American Journal of Opthalmology, Volume 81, No. 2, pages 232-235 (1976); Donowitz, U.S. Pat. No. 3,788,327; and Haas, U.S. Pat. No. 4,402,681. The Krupin article discloses numerous attempts at solving the problems associated with permanent seton installation requirements, such as friction between the eyelids, extraocular muscles and other ocular adnea with the device, overly complicated construction and overly difficult surgical implantation techniques, as well as problems with frequent need for additional post-operative invasive surgical procedures to address post-operative complications. However, the Krupin device and all others with valves in the tube which connect the plate with the anterior chamber are routinely associated with obstruction of the valve by fibroblasts which render the device useless because of an unapproachable obstruction to aqueous flow out of the eye.
A number of other devices and related surgical procedures designed by Krupin, White, and others exist for the drainage of aqueous humor to reduce intraocular pressure as a means of treating glaucoma. All of these disclose a tube or shunt for draining aqueous humor from the anterior chamber of the eye. Many current devices require the surgeon to place an external suture on the silastic tube to prevent early post-operative hypotony, or the procedure is divided into two stages to prevent the problem of early post-operative low intraocular pressure.
A number of these devices also disclose valves for controlling drainage or for preventing backflow. In the U.S. Pat. No. 4,554,918 to White, for example, an intraocular pressure relief device is disclosed which describes the use of a conduit to drain aqueous humor from the anterior chamber, a reservoir for holding fluid, thereby drained, and a check valve to prevent backflow. The problem with this device is that the reservoir is emptied by manual manipulation, which is both inefficient and uncomfortable for the patient. It also increases significant potential risk of extrusion due to frequent manipulation and has therefore been discarded by all but a few surgeons.
Similarly, U.S. Pat. No. 4,729,761 discloses a glaucoma implant device that also relies on the patient to pump aqueous cut of a drainage reservoir. Patient manipulation, as delineated above, is uncomfortable, inefficient and increases potential for extrusion as well as breakdown of surrounding tissue which can present catastrophic complications, such as endophthalmitis, associated with the use of the devices.
Additionally, the valves which are placed in the silastic tubing of these other implant devices to prevent hypotony in the early peri-operative period are almost universally fibrosed by pleuripotential macrophages. These are cells which are found in the anterior chamber of the eye. After surgery, these cells drain through the tube shunt, attach to the valve and, through a process of fibrosis, obstruct the tube at the site of the valve thereby making the device inoperative.
The present invention improves upon the prior art of glaucoma implant devices. One object of the present invention is to provide an implant device and related surgical procedure for treating glaucoma by reducing intraocular pressure on a regular basis without significant post-operative complications and which also will result in long-term successful shunting of fluid from the anterior chamber into the orbit of the eye.
Another object of the invention is to provide a glaucoma implant device which is biocompatible with the human eye, both through the materials used in the structure of the device and through its shape following the natural contours of the eye and ocular adnea.
Another object of the present invention is to provide an implant device and related surgical procedure for treating glaucoma using a device which is quickly adapted to varying eye sizes of patients, which does not require extensive surgeon time either before surgery to customize each implant to fit a patient to be operated upon, during surgery through extensive incision, suturing, placement or other surgical procedures required to implant the device, or after implantation by requiring additional corrective surgery or other labor intensive monitoring of the implant.
Another object of the invention is to provide a glaucoma implant device and related surgical procedure whereby installation of the device involves a minimal interruption of normal tissues and, preferably, disturbs only one quadrant of the globe.
Yet another object of the invention is to provide a glaucoma implant device which is accessible and ready for implantation as a pre-manufactured, single-piece device to facilitate uniform quality of the device before surgery, to ensure that the device is uniform for any successive surgical procedure, and to facilitate its implantation, thereby eliminating the requirement that the device be used only by the most highly skilled surgeons.
Still another object of the present invention is to provide a glaucoma implant device having a pre-placed ligature to prevent early post-operative hypotony.
Another object of the invention is to provide a glaucoma implant device which is free of any valves which present opportunities for obstruction of the tube shunt by the natural healing mechanisms available to the body, such as pleuripotential macrophages.
Yet another object of the invention is to provide an implant device and related surgical procedure for treating glaucoma whereby complications of glaucoma implant surgery are minimized using design features of the implant, which features are quickly implemented by the surgeon with minimal discomfort or risk of complication to the patient, including but not limited to making the device of a flexible, biocompatible material, markings placed on the tube shunt to facilitate precise and accurate placement of the tube within the anterior chamber of the eye, and minimal suturing of the device onto the sclera while still achieving stable implantation through special design features of the device.
Another object of the invention is to provide a glaucoma implant device of sufficient surface area to supply an adequate cavity for reception of aqueous humor and thereby allow appropriate diffusion of the fluid from the anterior chamber into the orbital tissues.